The present invention relates generally to tillage implements and more specifically to a heavy duty spring trip standard assembly.
Spring trip standard assemblies, particularly chisel plow standard assemblies, typically are designed to have large increases in trip force as the shank trips upwardly and rearwardly to clear an obstacle. The force at maximum trip height is typically three to five times the initial trip force. This large increase in trip force requires a very strong and heavy frame to carry the maximum trip force developed by the standard. To lower the maximum trip force of a conventional spring trip standard assembly requires lowering the initial trip force. However, a low initial trip force decreases implement stability and results in unwanted tripping of the standard. High initial trip forces are required with tillage implements which are towed by high horsepower tractors in order to maintain deep penetration of the earthworking tool, particularly at relatively high ground speeds since draft increases with ground speed.
Although spring trip standard assemblies utilizing a leaf-spring structure have been available, such structure has required a longer than normal horizontal portion on the shank and a relatively tall rear bracket extending upwardly from the rear of the shank to accommodate the leaf spring and provide the geometery necessary for a trip force which is initially high and which decreases as the tool is pushed higher. An example of such structure may be found in the automatic reset system on the commercially available Kvernelands plows and chisel plows produced by Kvernelands Fabrikk A/S of Kverneland, Norway. Other standard assemblies, such as shown in U.S. Pat. No. 2.906,353 issued to I. C. Rogers, utilize a pair of telescoping spring-strut units to provide relatively high initial trip force. The telescoping units are expensive and are subject to binding.
Some spring trip standard assemblies, such as the aforementioned Kverneland and Rogers assemblies, require down-stops to establish the working depth of the shank and have brackets which are constantly loaded by the spring. Therefore, the support structure must be strong enough to accommodate the constant spring load. The spring load must be removed to disassemble the structure.